The SpaceX team conducted a successful Wet Dress Rehearsal (WDR) on their Falcon 9 launch vehicle at Cape Canaveral on Thursday. The Launch Readiness Test was a major milestone ahead of the launch vehicle’s role to loft Dragon into orbit and en route to the International Space Station (ISS) late in April.

SpaceX Falcon 9 WDR:

Thursday’s test was – as the title suggests – a full dress rehearsal of the countdown for the real event of launching the Falcon 9 with the Dragon spacecraft.

Falcon 9 is a two stage rocket, with both stages burning RP-1 propellant with liquid oxygen oxidiser. The first stage is powered by nine Merlin 1C engines, whilst the second is powered by a single Merlin Vacuum engine.

As with a real launch day countdown, the business end of procedures and checks began two hours and thirty five minutes before launch, with flight controllers being polled to begin the fuelling of the rocket.

The strongback – a structure used to transport the rocket to the pad, raise it to vertical, and support it – was lowered at around the L-100 minute point. Fuel and thrust vector control bleeding on the second stage was then performed at T-1 hour. At T-13 minutes, a final flight readiness poll was conducted, which was followed by the final hold point at T-11 minutes.

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The terminal count began ten minutes before launch, followed by the rocket being transferred to internal power at four minutes and forty six seconds before launch. The flight termination system, used to destroy the rocket in the event of a problem during an actual launch, was armed three minutes and eleven seconds before launch, and seven seconds later oxidiser topping ended.

The flight computer was started sixty seconds before launch, ahead of the pad water system being activated. This would normally be followed by the pressurization of the propellant tanks. However, during this initial attempt, the countdown was held around one minute to T-0 due to an unknown issue.

While a hold at this stage of the countdown would have likely resulted in a scrub for the day during an actual launch, the problem is understood to be minor, not least because the SpaceX team recycled the countdown back to T-10 minutes and this time proceeded through to the pressurization tasks at T-40 seconds.

As scheduled, the countdown went down to the T-5 second mark, successfully concluding the WDR milestones.

“Today SpaceX held a launch readiness test including the full countdown procedures for the upcoming test flight,” noted SpaceX communications director Kirstin Brost Grantham. “We ran down the countdown clock to a planned abort at T-5 seconds at 12:18 PM eastern. The test went well.

“Over the coming days we will continue to review the data as we prepare for our upcoming mission.”

SpaceX also confirmed the WDR satisfied all of their data points, allowing them to press on towards the launch date, with the next milestone likely to be a static fire of the Falcon 9’s engines a few days prior to launch.

The Californian company also noted to NASASpaceflight.com that the Falcon 9 will be lowered to its horizontal level via the strongback and rolled back to its integration hanger on Friday, after a late cargo load test with NASA teams is completed later on Thursday.

Thursday’s WDR also provided teams at the Space X and JSC’s Mission Control Center’s (MCC-X and MCC-H) the opportunity of running a “mission based simulation” in paralell with the the projected T-0.

Should the mission proceed as planned, the Dragon will mark a historic milestone, becoming the first commercial spacecraft to dock with the orbital outpost, opening a new chapter where private companies take over the United States’ requirements in Low Earth Orbit (LEO), allowing NASA to refocus on a return to deep space exploration.

The primary objectives for Dragon’s C2/C3 flight include a fly-by of the space station at a distance of approximately two miles to validate the operation of sensors and flight systems necessary for a safe rendezvous and approach.

Should Dragon pass these milestones, the spacecraft will perform the final approach to the ISS ahead of the station crew grappling the vehicle with the SSRMS (Space Station Remote Manipulator System), allowing it to be berthed with the Earth-facing side of the Harmony node.